(class viii) exercise 1 - mywayteaching.commywayteaching.com/math_classviii/solutionm8-1.pdf13 2 2...

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(Class – VIII)

Exercise 1.1 Question 1:

Using appropriate properties find:

(i) 2 3 5 3 1

3 5 2 5 6

(ii) 2 3 1 3 1 2

5 7 6 2 14 5

Answer 1:

(i) 2 3 5 3 1

3 5 2 5 6 =

2 3 3 1 5

3 5 5 6 2 [Using associative property]

= 3 2 1 5

5 3 6 2

[Using distributive property]

= 3 4 4 5

5 6 2

=

3 5 5

5 6 2

= 1 5

2 2 =

1 5

2

=

4

2 = 2

(ii) 2 3 1 3 1 2

5 7 6 2 14 5

= 2 3 1 2 1 3

5 7 14 5 6 2

[Using associative property]

= 2 3 1 1

5 7 14 4

[Using distributive property]

= 2 6 1 1

5 14 4

= 2 5 1

5 14 4

= 1 1

7 4

=

4 7

28

=

11

28

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Math Class 8 Chapter 1-NCERT Solution 8/10 Email:[email protected]

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(Class – VIII)

Question 2:

Write the additive inverse of each of the following:

(i) 2

8

(ii) 5

9

(iii) 6

5

(iv) 2

9

(v) 19

6

Answer 2:

We know that additive inverse of a rational number a

b is ,

a

b

such that 0.a a

b b

(i) Additive inverse of 2

8 is

2.

8

(ii) Additive inverse of 5

9

is

5.

9

(iii) Additive inverse of 6

5

is

6.

5

(iv) Additive inverse of 2

9 is

2.

9

(v) Additive inverse of 19

6 is

19.

6

Question 3:

Verify that x x for:

(i) 11

15x (ii)

13

17x

Answer 3:

(i) Putting 11

15x in ,x x



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(Class – VIII)

11 11

15 15

11 11

15 15

L.H.S. = R.H.S.

Hence, verified.

(ii) Putting 13

17x

in ,x x

13 13

17 17

13 13

17 17

L.H.S. = R.H.S.

Hence, verified.

Question 4:

Find the multiplicative inverse of the following:

(i) 13

(ii) 13

19

(iii) 1

5

(iv) 5 3

8 7

(v) 2

15

(vi) 1

Answer 4:

We know that multiplicative inverse of a rational number a is 1

,a

such that 1

1.aa

(i) Multiplicative inverse of 13 is 1

.13

(ii) Multiplicative inverse of 13

19

is

19.

13



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(Class – VIII)

(iii) Multiplicative inverse of 1

5 is 5.

(iv) Multiplicative inverse of 5 3 15

8 7 56

is

56.

15

(v) Multiplicative inverse of 2 2

15 5

is

5.

2

(vi) Multiplicative inverse of 1 is 1

.1

Question 5:

Name the property under multiplication used in each of the following:

(i) 4 4

1 15 5

(ii) 13 2 2 13

17 7 7 17

(iii) 19 29

129 19

Answer 5:

(i) 1 is the multiplicative identity.

(ii) Commutative property.

(iii) Multiplicative Inverse property.

Question 6:

Multiply 6

13 by the reciprocal of

7.

16

Answer 6:

The reciprocal of

7

16

is

16.

7

According to the question,

6 16

13 7

= 96

91



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(Class – VIII)

Question 7:

Tell what property allows you to compute 1 4

63 3

as 1 4

6 .3 3

Answer 7:

By using associative property of multiplication, a b c a b c .

Question 8:

Is 8

9 the multiplicative inverse of

11 ?

8 Why or why not?

Answer 8:

Since multiplicative inverse of a rational number a is 1

,a

if 1

1.aa

Therefore, 8 1

19 8

= 8 9

9 8

= 1

But its product must be positive 1.

Therefore, 8

9 is not the multiplicative inverse of

11 .

8

Question 9:

Is 0.3 the multiplicative inverse of 1

3 ?3

Why or why not?

Answer 9:

Since multiplicative inverse of a rational number a is 1

,a

if 1

1.aa

Therefore, 1

0.3 33

= 3 10

10 3 = 1

Therefore, Yes 0.3 is the multiplicative inverse of 1

3 .3



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(Class – VIII)

Question 10:

Write:

(i) The rational number that does not have a reciprocal.

(ii) The rational numbers that are equal to their reciprocals.

(iii) The rational number that is equal to its negative.

Answer 10:

(i) 0

(ii) 1 and 1

(iii) 0

Question 11:

Fill in the blanks:

(i) Zero has _______________ reciprocal.

(ii) The numbers _______________ and _______________ are their own reciprocals.

(iii) The reciprocal of 5 is _______________.

(iv) Reciprocal of 1

,x

where 0x is _______________.

(v) The product of two rational numbers is always a _______________.

(vi) The reciprocal of a positive rational number is _______________

Answer 11:

(i) No

(ii) 1, 1

(iii) 1

5

(iv) x

(v) Rational Number

(vi) Positive



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(Class – VIII)

Exercise 1.2 Question 1:

Represent these numbers on the number line:

(i) 7

4(ii)

5

6

Answer 1:

(i) 7 3

14 4

Here, P is 3 7

14 4

(ii) 5

6

Here, M is 5

6

Question 2:

Represent 2 5 9

, ,11 11 11

on the number line.

Answer 2:

Here, B = 2

,11

C =

5

11

and D =

9

11



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(Class – VIII)

Question 3:

Write five rational numbers which are smaller than 2.

Answer 3:

1 1 1 1 1, , , ,

3 4 2 2 5

and so on.

Question 4:

Find ten rational numbers between 2

5

and

1.

2

Answer 4:

Given rational numbers 2

5

and

1

2

Here, L.C.M. of 5 and 2 is 10.

2 2 4

5 2 10

and

1 5 5

2 5 10

Again, 4 2 8

10 2 20

and

5 2 10

10 2 20

Ten rational number between 2

5

and

1

2 are

7 6 5 4 3 2 1 1 2, , , , , , ,0, ,

20 20 20 20 20 20 20 20 20

.

Question 5:

Find five rational numbers between:

(i) 2

3 and

4

5(ii)

3

2

and

5

3(iii)

1

4 and

1

2

Answer 5:

(i) 2

3 and

4

5



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(Class – VIII)

L.C.M. of 3 and 5 is 15.

2 5 10

3 5 15 and

4 3 12

5 3 15

Again 10 4 40

15 4 60 and

12 4 48

15 4 60

Five rational numbers between 2

3 and

4

5 are

41 42 43 44 45, , , ,

60 60 60 60 60.

(ii) 3

2

and

5

3


3 3 9

2 3 6

and

5 2 10

3 2 6


2

and

5

3 are

8 7 1 2, ,0, ,

6 6 6 6

.

(iii) 1

4 and

1

2


1 1 1

4 1 4 and

1 2 2

2 2 4

Again 1 8 8

4 8 32 and

2 8 16

4 8 32


4 and

1

2 are

9 10 11 12 13, , , , .

32 32 32 32 32

Question 6:

Write 5 rational numbers greater than 2.

Answer 6:

Five rational numbers greater than 2 are:

3 1 1, 1, ,0,

2 2 2

[Other rational numbers may also be possible]



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(Class – VIII)

Question 7:

Find ten rational numbers between 3

5 and

3.

4

Answer 7:

The given rational numbers 3

5 and

3

4


3 4 12

5 4 20 and

3 5 15

4 5 20

Again 12 8 96

20 8 160 and

15 8 120

20 8 160


5 and

3

4 are:

97 98 99 100 101 102 103 104 105 106, , , , , , , , ,

160 160 160 160 160 160 160 160 160 160



(class viii) exercise 1 - mywayteaching.commywayteaching.com/math_classviii/solutionm8-1.pdf13 2 2...

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